Generally, the mirror polishing of semiconductor wafers such as a silicon wafer etc., lenses, and glass substrates includes rough polishing primarily intended to regulate planarity and in-plane uniformity and final polishing primarily intended to improve surface roughness and removal of scratches.
The final polishing is carried out usually by rubbing a wafer against an artificial suede made of flexible urethane foam stuck to a rotatable platen and simultaneously feeding thereon an abrasive containing a colloidal silica in an alkali-based aqueous solution (Patent Literature 1).
As the polishing pad for finishing used in final polishing, the following polishing pads have been proposed besides those described above.
A suede finishing polishing pad comprising a nap layer having a large number of long and thin holes (naps) formed with a foaming agent in the thickness direction, in polyurethane resin, and a foundation cloth for reinforcing the nap layer is proposed (Patent Literature 2).
A suede abrasive cloth for final polishing, in which surface roughness is expressed as an arithmetic average roughness (Ra) of 5 μm or less, is proposed (Patent Literature 3).
An abrasive cloth for final polishing, which is provided with a base material part and a surface layer (nap layer) formed on the base material part, wherein a polyvinyl halide or vinyl halide copolymer is contained in the surface layer, is proposed (Patent Literature 4).
Conventional polishing pads for finishing have been produced by a wet curing method. The wet curing method is a method wherein an urethane resin solution obtained by dissolving urethane resin in a water-soluble organic solvent such as dimethylformamide is applied onto a base material, then wet-solidified by treatment in water, to form a porous grain side layer, which is then washed with water and dried, followed by polishing of the grain side layer to form a surface layer (nap layer). In Patent Literature 5, for example, an abrasive cloth for finishing, having roughly spherical holes having an average particle diameter of 1 to 30 μm, is produced by the wet curing method.
In the wet curing method, however, there is a problem that a large amount of metal impurity-free purified water should be used, tremendous investment in plant and equipment is necessary, and production costs are very high. Because a solvent should be used, there is another problem of high environmental burden. In the conventional polishing pads, cells have a thin and long structure, or the material of the surface layer itself is poor in mechanical strength, and thus there are problems such as poor durability, gradual deterioration in planarizing characteristics, and inferior stability of removal rate. In addition, the conventional polishing pads have a problem of easy interfacial release of a polishing layer from a base material layer because of low adhesion therebetween. The conventional polishing pads have a problem of easy clogging on the surface of the pad during polishing because of interior self-dressing.    Patent Literature 1: JP-A 2003-37089    Patent Literature 2: JP-A 2003-100681    Patent Literature 3: JP-A 2004-291155    Patent Literature 4: JP-A 2004-335713    Patent Literature 5: JP-A 2006-75914